Stock Incentive Plans - Restricted Stock (Details) - Restricted Stock [Member] - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock expense	$ 28.0	$ 20.7	$ 25.8
Restricted stock expense, net of tax	$ 20.4	$ 15.1	$ 18.8
Status of nonvested restricted stock [Roll Forward]
Nonvested shares subject to restriction, beginning balance	1,266,000	1,411,000	2,064,000
Nonvested shares subject to restriction, weighted average price, beginning balance	$ 43.57	$ 37.86	$ 29.39
Nonvested shares subject to restriction, granted	687,000	447,000	782,000
Nonvested shares subject to restriction, weighted average price, granted	$ 58.45	$ 54.36	$ 37.82
Nonvested shares subject to restriction, vested	(588,000)	(530,000)	(1,322,000)
Nonvested shares subject to restriction, weighted average price, vested	$ 39.14	$ 37.42	$ 24.36
Nonvested shares subject to restriction, forfeited	(39,000)	(62,000)	(113,000)
Nonvested shares subject to restriction, weighted average price, forfeited	$ 50.85	$ 41.14	$ 36.59
Nonvested shares subject to restriction, ending balance	1,326,000	1,266,000	1,411,000
Nonvested shares subject to restriction, weighted average price, ending balance	$ 53.18	$ 43.57	$ 37.86
Restricted stock unrecognized compensation, amount	$ 33.2
Restricted stock unrecognized compensation, period	2 years
Management [Member]
Status of nonvested restricted stock [Roll Forward]
Nonvested shares subject to restriction, granted	669,754
Director [Member]
Status of nonvested restricted stock [Roll Forward]
Nonvested shares subject to restriction, granted	16,983